The present invention relates to an adhesive-backed article, more particularly to such an adhesive-backed article having an adhesive with a microstructured surface bonded to a compliant film, and even more particularly to channels, with a specific volume per unit area, formed by the microstructured surface in the adhesive which permit the desirable properties of positionability and fluid egress to a periphery of the article without adversely affecting the surface appearance of the film after application onto a substrate.
Films are often bonded to substrates utilizing pressure-sensitive adhesives. The films are generally bonded to a variety of different substrates including, for example, surfaces on motor vehicles. The interface between the adhesive and the contact surface of the substrate is important to the performance of the film. The interface between the adhesive and the substrate is affected by several factors. For example, the application may be affected by the type of adhesive used, the size and type of the films utilized, the surface of the substrate upon which the article is applied, the application technique utilized, or combinations thereof.
Adhesive-backed films are often used for decorative purposes. The placement of a film into a specific position prior to the formation of a bond between the adhesive and the substrate is often difficult, but important for aesthetic reasons. Some adhesive-backed articles are unable to slide on the surface of the substrate and will adhere with the slightest contact on the surface of the substrate. Such articles can often be particularly difficult to reapply if they inadvertently adhere to the substrate. The inability to slide the adhesive-backed article in place can adversely affect the positioning of the article or cause damage to the article upon attempted repositioning after adhesion.
The decorative articles also require that the adhesive-backed article be able to evacuate air or other fluids trapped underneath the adhesive during the bonding step. The ability to bleed fluids and eliminate bubbles from underneath the article improves the overall appearance of the article. Additionally, bubbles under a film can adversely affect the adhesive performance of the article.
Thin films are often utilized on surfaces so that the adhesive film blends with the substrate upon which the film is applied. Additionally, thinner films are generally more flexible and therefore suited for application on contoured surfaces. However, the utilization of thin films can create an appearance problem. The thinner films have a tendency to show all surface abnormalities or uneven portions of either the adhesive or the substrate upon which the adhesive-backed article is applied.
The present invention relates to an adhesive-backed article. The article includes a compliant film with a pressure sensitive adhesive bonded to a lower surface of the film. The pressure sensitive adhesive includes a microstructured surface opposite the compliant film.
In accordance with the present invention, the microstructured surface defines channels in the pressure sensitive adhesive. The channels comprise a volume of at least 1xc3x97103 xcexcm3 per any 500 xcexcm diameter circular area in the adhesive. The channels are utilized to create exit pathways for fluid egress to a periphery of the article when the article is applied to a substrate. The adhesive-backed article sufficiently bonds to a substrate as indicated by a wet out value of at least 85%. The channels are substantially undetectable on an upper surface after final application of the article onto a substrate.
In general, the adhesive-backed article of the present invention is positionable over a substrate prior to forceful application of the article onto the substrate. The microstructured surface of the adhesive permits the article to either slide over the surface of a substrate, or be easily removed from the surface of the substrate, until enough pressure is applied to enable a bond between the adhesive and the surface of the substrate. The article of the present invention also enhances the egress of fluid from the interface between the adhesive and the substrate as a bonding force is applied to the article. The microstructured features are particularly suited for applications utilizing thin films, ie less than 300 xcexcm.
The channels of the present invention can take various shapes or patterns. The channels are generally formed by structures in the adhesive that create the microstructured surface. The structures may be either placed randomly about the surface of the adhesive or placed in regular patterns.
The microstructured surface can be formed by directly embossing the pressure sensitive adhesive layer with the structures. Alternatively, a liner or backing can be embossed first and then coated with a pressure sensitive adhesive to impart the structures to the adhesive. The film is typically laminated or bonded to a side of the adhesive layer opposite the microstructured features.
It is an advantage to provide an adhesive-backed article that has pathways in the adhesive for fluid egress and permits positioning of the article without adversely affecting the appearance of the article. The channels define pathways to the periphery of the article that permit the flow of fluid trapped between the adhesive and the surface of the substrate. Additionally, the microstructured surface of the present invention enable the positioning of the article onto a substrate. Further, the microstructured adhesive does not result in observable periodic patterns on the exposed surface of the film after application of the article onto a substrate.
For purposes of the present invention, the following terms used in this application are defined as follows:
xe2x80x9cmicroscopicxe2x80x9d refers to structures of small enough dimension so as to require an optic aid to the naked eye when viewed from any plane of view to determine its shape. One criterion is found in Modern Optic Engineering by W. J. Smith, McGraw-Hill, 1966, pages 104-105 whereby visual acuity, xe2x80x9c . . . is defined and measured in terms of the angular size of the smallest character that can be recognized.xe2x80x9d Normal visual acuity is considered to be when the smallest recognizable letter subtends an angular height of 5 minutes of arc on the retina. At typical working distance of 250 mm (10 inches), this yields a lateral dimension of 0.36 mm (0.0145 inch) for this object;
xe2x80x9cmicrostructurexe2x80x9d means the configuration of structures wherein at least 2 dimensions of the structures are microscopic. The topical and/or cross-sectional view of the structures must be microscopic.;
xe2x80x9cembossablexe2x80x9d refers to the ability of a pressure-sensitive adhesive layer or liner to have part of its surface raised in relief, especially by mechanical means;
xe2x80x9cwettingxe2x80x9d or xe2x80x9cwet outxe2x80x9d means spreading out over and intimately contacting a surface;
xe2x80x9cpositionablexe2x80x9d or xe2x80x9cpositionabilityxe2x80x9d refers to those adhesive-backed articles that can easily slide over a substrate without grabbing or bonding to the substrate absent the application of a force, or adhesive-backed articles that upon light force are capable of releasably bonding to a substrate and upon removal retain at least some form of the original microstructured surface;
xe2x80x9crelease linerxe2x80x9d, used interchangeably with the term xe2x80x9clinerxe2x80x9d, refers to a flexible sheet which after being placed in intimate contact with pressure-sensitive adhesive surface may be subsequently removed without damaging the adhesive coating;
xe2x80x9cmicrostructured linerxe2x80x9d refers to a liner with at least one microstructured surface, which is suitable for contact with an adhesive;
xe2x80x9cbackingxe2x80x9d refers to a thin, flexible sheet which, after being placed in intimate contact with pressure-sensitive adhesive can not be subsequently removed without damaging the adhesive coating;
xe2x80x9cmicrostructured backingxe2x80x9d refers to a backing with a microstructured surface.
xe2x80x9csubstratexe2x80x9d refers to a surface to which the pressure-sensitive adhesive coating is applied for an intended purpose;
xe2x80x9ctapexe2x80x9d refers to a pressure-sensitive adhesive coating applied to a backing.
xe2x80x9cinelastic deformationxe2x80x9d means the permanent set at a given strain resulting from a film being stretched to 15% under tension and dissipating that tension.
xe2x80x9ccompliantxe2x80x9d refers to a polymeric film that is soft and flexible as well as having sufficient inelastic deformation after being stretched so that once stretched, the film does not recover to its original length;
xe2x80x9cbleedabilityxe2x80x9d or xe2x80x9cair-bleedabilityxe2x80x9d refers to the egress of fluids, particularly air, from the interface between the adhesive and the surface of the substrate; and
xe2x80x9cappearancexe2x80x9d means the visual characteristics of the article as viewed from the exposed surface of the film after application of the article onto a substrate.